The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
A Transimpedance Amplifier (TIA) is a current-to-voltage converter. In the field of fiber optics, TIAs are used to produce voltage differentials that correspond to digital data.
In optical receiver applications, a Transimpedance Amplifier (TIA) is typically housed in an optical sub-assembly (e.g. TO-can package), which is limited to 5 or 6 pins. Those pins are VDD, VSS, OUTP, OUTN, RSSI, and PINK (for 6 pin TO-cans). One problem is that the typical configuration fails to leave any of the standard pins for control interface. Without a control interface, the settings of the TIA cannot be adjusted to optimize them for a particular application and/or environment.
As used herein, the term “pin” is used to denote an electrical connection, of whatever physical nature. Thus, the term “pin” should be interpreted herein to also include connections physically configured as pads.
Some previous devices have used additional bond-pads for controlling a few of the settings. However, the number of additional bond-pads for control settings is limited to 2 to 4 pads because of constraints in the size/area of the chip. Thus, the number of different settings is limited to 2 to 4, which constrains optimization, and in some cases/applications limits the use of the TIA.
When driving lasers, control circuits frequently need to adjust the input in order to compensate for changes in the environment. For example, U.S. Pat. No. 8,903,246 to Wieland devotes some sub-assembly pins to operating a control interface inside a sub-assembly. However, diverting use of those pins from conventional functionalities to control functions eliminates those conventional functionalities.
US 2004/0145799 to Sedic teaches a system that adjusts a transimpedance amplifier (TIA) with a controller that communicates a selected mode of operation to the TIA. Each selected mode can adjust at least one of the TIA's operational settings, such as a transimpedance gain, bandwidth, DC offset, signal rise and fall time, power consumption, and output impedance. Sedic's system, however, requires a controller to be pre-configured for operation modes, and does not allow for fine-tuning of each of the settings independently from one another, which may be necessary for unforeseen needed modifications to a TIA.
Thus, there is still a need for systems and methods that can modify functioning of a TIA for different conditions and/or applications, without sacrificing conventional functionality of the existing pins/pads.